1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and a method for producing the electrophotographic photosensitive member, and to a process cartridge and an electrophotographic apparatus including the electrophotographic photosensitive member.
2. Description of the Related Art
In recent years, electrophotographic photosensitive members (organic electrophotographic photosensitive members) including a charge generating layer that contains a charge generating substance and a charge transporting layer that contains a charge transporting substance have been used as electrophotographic photosensitive members used for electrophotographic apparatuses.
The potential characteristics (chargeability and sensitivity) of the electrophotographic photosensitive member depend on the types of materials used for the charge generating layer and the charge transporting layer. Thus, the potential characteristics of the electrophotographic photosensitive member can be improved by changing the structures and combination of the above-described materials.
With a recent increase in the processing speed of electrophotographic apparatuses, in addition to the improvement in potential characteristics such as increases in chargeability and sensitivity, the potential variation (changes in chargeability and sensitivity) after repeated use needs to be further suppressed. Specifically, the potential variations (changes in chargeability and sensitivity) in terms of (1) and (2) below need to be further suppressed:
(1) Long-term repeated use from the initial use of an electrophotographic photosensitive member to the end of the life of the electrophotographic photosensitive member; and
(2) Relatively short-term repeated use (e.g., from the first image output to the completion of about 1000 continuous outputs).
In terms of (1) above, the potential variation may be increased depending on the configuration of the electrophotographic photosensitive member (the potential characteristics may be significantly degraded). In such a case, even if the electrophotographic photosensitive member is left to stand after long-term repeated use, the potential characteristics do not return to the original level, which means low recoverability.
In the case where the potential variation is large in terms of (2) above, for example, the color of an image formed on the first output sheet sometimes becomes different from that of an image formed on the 1000th output sheet. However, in such a short-term potential variation, the potential characteristics easily return to the original level within a relatively short time by leaving the electrophotographic photosensitive member.
It is believed that the potential variation of (1) is caused by accumulating the potential variations of (2) that are not recovered within a short time even if the electrophotographic photosensitive member is left to stand.
It is important to suppress the potential variations of (1) and (2) above and thus allow an electrophotographic photosensitive member to always stably output an image. In particular, the potential variation of (2) above is problematic, and the change in color needs to be small in any circumstances.
In other words, the potential variation of (2) above at the beginning of use of an electrophotographic photosensitive member needs to be suppressed, or the potential variation of (2) above after the long-term repeated use of the electrophotographic photosensitive member needs to be suppressed.
Japanese Patent Laid-Open No. 2-97961 discloses a technology that suppresses a potential variation by adding a certain fluorenone compound to the charge generating layer of an electrophotographic photosensitive member. However, Japanese Patent Laid-Open No. 2-97961 does not focus on the potential variation of (2) above.
In fact, the electrophotographic photosensitive member disclosed in Japanese Patent Laid-Open No. 2-97961 had a small potential variation of (2) when used for a short time at the beginning of use of the electrophotographic photosensitive member. However, when a short-term potential variation ((2) above) after the long-term repeated use ((1) above) of the electrophotographic photosensitive member was measured, the potential variation was increased compared with the initially measured potential variation.
Regardless of the degree of potential variation after long-term repeated use, the short-term potential variation after the long-term repeated use was increased compared with the initially measured short-term potential variation.
The fluorenone compound disclosed in Japanese Patent Laid-Open No. 2-97961 easily caused spot-like image defects on an output image when used for a charge generating layer containing polyvinyl acetal as a binder resin. This phenomenon also occurred considerably when a charge-generating-layer coating solution was stored in a high-temperature environment.